Transmission rate control method for avoiding interference in radio communications

ABSTRACT

A communication apparatus includes an RF signal processing circuit for processing a received RF signal, an RF demodulating circuit for demodulating an output signal of the RF signal processing circuit, a decoding circuit for decoding an output signal from the RF demodulating circuit, an encoding circuit for encoding a predetermined information signal, an RF modulating circuit for modulating an output signal from the encoding circuit, and a transmission signal processing circuit for processing an output signal from the RF modulating circuit. The encoding circuit includes a memory for storing predetermined control data, a selecting circuit for selecting the predetermined control data in accordance with an information of circuit quality obtained from the decoding circuit, and an adding circuit for adding the transmission data with an output of the selecting circuit. An output power of the transmission signal processing circuit is controlled by the information of the circuit quality.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication method suitable forapplication to a base station and a terminal apparatus of a radiotelephone system, for example, and a base station and a terminalapparatus to which the communication method is applied.

2. Description of the Related Art

In a mobile communication system such as a radio telephone system or thelike, multiple access where a plurality of mobile stations (terminalapparatus or subscribers) are permitted to access a single base stationis employed. In the case of a radio telephone, a number of mobilestations commonly utilize a single base station. Therefore, variouscommunication systems have been proposed for avoiding interferencebetween respective mobile stations. For example, a frequency divisionmultiple access (FDMA) system, a time division multiple access (TDMA)system, a code division multiple access (CDMA) system and so on areconventionally proposed as this kind of communication systems.

Of these systems, the CDMA system is a multiple access system in which aparticular code is assigned to each of the mobile stations, a modulatedwave of an identical carrier wave (carrier) is spread in spectrum withthe code and then transmitted to the identical base station, and a basestation receives it with taking code synchronism based on each code toidentify a desired mobile station.

Specifically, the base station occupies the whole frequency band owingto the spectrum, and transmits signals to a plurality of mobile stationsusing an identical frequency band at the same time. Each of the mobilestations inversely spreads a signal of a fixed spread band widthtransmitted from the base station to extract a corresponding signal.Further, the base station discriminates each of the mobile stations bydifferent spread codes from one another.

In the CDMA system, communication can be achieved at every directcalling so long as a code is shared. Further, the system is excellent insecrecy of telephone conversation. Therefore, the system is suitable fora radio transmission utilizing mobile stations such as a portabletelephone apparatus and so on.

The assignee of the present application has proposed a communicationsystem called a band division multiple access (BDMA) system (disclosedin Japanese patent application No. 132434/1996 and so on) as anothercommunication system. While details of the BDMA system will be describedin the detailed description of the preferred embodiment later on, theBDMA system is as follows in short. A plurality of transmission bands ineach of which subcarrier signals of a predetermined number are disposedat a predetermined frequency interval are prepared. A signal in each ofthe transmission bands is divided by every predetermined time to formtime slots. A burst signal is transmitted in the form of a multicarriersignal modulated by dispersing the signal intermittently into thesubcarrier signals of the above predetermined number at a period of thetime slots of a predetermined number. This BDMA system has excellenttransmission characteristics.

A system having a frequency allocation called one-cell repetition systemhas been proposed as a radio telephone system to which the abovecommunication systems is applied. In this one-cell repetition system, afrequency band used in a cell formed of each of base stations is madecommon in all the cells. In this case, since a frequency used in each ofthe cells is the same, there can be achieved an effect in which a systemarrangement used when the base stations are located to form cells isconsiderably simplified.

However, if the one-cell repetition system is employed, then the samefrequency is a used even in adjacent cells. Therefore, since there ishigh possibility that communication at one station will interfere withcells adjacent to the station, the one-cell repetition system can onlybe applied to a communication system having excellent selectivity of aspecific path such as the above CDMA system or the above BDMA system.

Moreover, even if the above CDMA system or the above BDMA system havingexcellent selectivity of a specific path is employed, it is frequentlyobserved that communication in one station interferes with cellsadjacent thereto depending upon the communication state.

SUMMARY OF THE INVENTION

In view of such aspects, it is an object of the present invention toprovide a communication method and a communication apparatus which canreduce interference of communication of adjacent cells to a minimum whena one-cell repetition system is applied.

According to a first aspect of the present invention, a communicationmethod in a predetermined band width with a predetermined format formultiple access by each cell, includes a detecting step of detecting aninterference to a communication between a first apparatus and a secondapparatus by communication of a third apparatus, and a lowering step oflowering an information transmission rate of said communication betweensaid first and second apparatus.

According to a second aspect of the present invention, a communicationapparatus communicating in a predetermined band width with apredetermined format for multiple access by each cell, includes a statusdetecting means for detecting a communication status for a predeterminedstation, and a rate adjusting means for lowering an informationtransmission rate of said communication when an output signal from saidstatus detecting means indicates that a level of a communication statusis lower than a predetermined value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram used to explain a slot arrangement of a transmissionsignal used in a communication apparatus according to an embodiment ofthe present invention;

FIGS. 2A to 2G are diagrams each used to explain a transmission state ina frame according to the embodiment;

FIGS. 3A to 3B are diagrams each used to explain an example of a bandslot arrangement according to the embodiment;

FIG. 4 is a block diagram showing an arrangement of a terminal apparatusaccording to an embodiment of the present invention;

FIG. 5 is a block diagram showing an arrangement of an encoder of theterminal apparatus according to the embodiment;

FIG. 6 is a block diagram showing an arrangement of a convolutionalencoder of the terminal apparatus according to the embodiment;

FIGS. 7A and 7B are diagrams showing examples of waveforms of awindowing data according to the embodiment;

FIG. 8 is a phase characteristic graph showing an example of atransmission data according to the embodiment;

FIG. 9 is a block diagram showing an arrangement of a decoder of theterminal apparatus according to the embodiment;

FIG. 10 is a timing chart showing a processing timing according to theembodiment;

FIG. 11 is a block diagram showing an arrangement of a base stationaccording to the embodiment;

FIG. 12 is a block diagram showing a modulation processing of the basestation according to the embodiment;

FIG. 13 is a block diagram showing a demodulation processing of the basestation according to the embodiment; and

FIG. 14 is a diagram used to explain a communication state according tothe embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A communication method and a communication apparatus according to anembodiment of the present invention will hereinafter be described withreference to FIG. 1 to FIG. 16.

Initially, a communication system to which the present embodiment isapplied will be described. The communication system of the presentembodiment is arranged as a so-called multicarrier system in which aplurality of subcarriers are continuously disposed within a bandallocated in advance, and the plurality of subcarriers within the singleband are utilized on a single transmission path at the same time.Further, the plurality of subcarriers within the single band arecollectively divided in the band to be modulated. Here, this system iscalled a band division multiple access (BDMA: Band Division MultipleAccess).

The arrangement thereof will be described below. FIG. 1 is a diagramshowing a slot arrangement of transmission signals of the presentembodiment in which a frequency is set in the ordinate thereof and atime is expressed on the abscissa thereof. In the present example, thefrequency-axis and the time-axis are divided in a lattice fashion toprovide an orthogonal base system. Specifically, the transmission bandwidth of one transmission band (one band slot) is set to 150 KHz and theone transmission band of the 150 KHz includes therein 24 subcarriers.The twenty-four subcarriers are disposed continuously with an equalinterval of 6.25 KHz, and every carrier is assigned with a subcarriernumber from 0 to 23. However, practically existing subcarriers areallocated to bands of subcarrier numbers of 1 to 22. Bands of both endportions of the one band slot, i.e., bands of subcarrier numbers of 0and 23 are assigned with no subcarrier, i.e., they are made to serve asa guard band and their electric power is set to zero.

One time slot is regulated at an interval of 200 μsec. in terms of thetime-axis. A burst signal is modulated and transmitted together with 22subcarriers at every time slot. One frame is defined as an array of 25time slots (i.e., 5 msec.). Each of the time slots within one frame isassigned with a time slot number from 0 to 24. A hatched area in FIG. 1represents a section of one time slot in one band slot. In this case, atime slot assigned with a slot number of 24 is a period in which no datais transmitted.

Multiple access in which a plurality of mobile stations (terminalapparatus) carry out communication with a base station at the sameperiod, is carried out by using the orthogonal base system which derivesfrom dividing the frequency-axis and time-axis in a lattice fashion.Connection condition with respective mobile stations is arranged asshown in FIGS. 2A to 2G. FIGS. 2A to 2G are diagrams each showing anoperation condition indicating that how six mobile stations areconnected to the base station by using time slots U0, U1, U2, . . . , U5with one band slot (actually utilized band slot is changed owing to afrequency hopping which will be described later). A time slotrepresented by R is a reception slot while a time slot represented by Tis a transmission slot. As shown in FIG. 2A, a frame timing regulated inthe base station is set to a period including 24 time slots (of the 25time slots, the last slot, i.e., a slot of number 24 is not utilized).In this case, the transmission slot is transmitted using a banddifferent from one of the reception slot.

The mobile station U0 shown in FIG. 2B uses time slots of time slotnumbers, 0, 6, 12, 18 within one frame as a reception slot, while timeslots of time slot numbers, 3, 9, 15, 21 as a transmission slot. A burstsignal is received or transmitted in each time slot. The mobile stationU1 shown in FIG. 2C uses time slots of time slot numbers, 1, 7, 13, 19within one frame as a reception slot, while time slots of time slotnumbers, 4, 10, 16, 22 as a transmission slot. The mobile station U2shown in FIG. 2D uses time slots of time slot numbers, 2, 8, 14, 20within one frame as a reception slot, while time slots of time slotnumbers, 5, 11, 17, 23 as a transmission slot. The mobile station U3shown in FIG. 2E uses time slots of time slot numbers, 3, 9, 15, 21within one frame as a reception slot, while time slots of time slotnumbers, 0, 6, 12, 28 as a transmission slot. The mobile station U4shown in FIG. 2F uses time slots of time slot numbers, 4, 10, 16, 22within one frame as a reception slot, while time slots of time slotnumbers, 1, 7, 13, 22 as a transmission slot. Further, the mobilestation U5 shown in FIG. 2G uses time slots of time slot numbers, 5, 11,16, 22 within one frame as a reception slot, while time slots of timeslot numbers, 2, 8, 14, 20 as a transmission slot.

In this embodiment, as described later on, a transmission rate ofcommunication between a base station and a mobile station (a terminalapparatus) can be changed. A processing for changing the transmissionrate is to change the number of time slots used on one path, forexample. Therefore, allocation of the time slots shown in FIGS. 2A to 2Gis normal allocation used when the transmission rate is set high. If thetransmission rate is set low, a time slot allocated to a mobile stationU0 shown in FIG. 2B and a time slot allocated to a mobile station U1shown in FIG. 2C are used by one mobile station to thereby secure twosuccessive time slots as a transmission slot T and also two successivetime slots as a reception slot R. Thus, a processing for doubling thenumber of time slots to be used when the same amount of information isto be transmitted. In accordance with this processing, the transmissionrate is lowered to 1/2. Accordingly, if a path in which the transmissionrate is set low is used, the number of mobile stations which cansimultaneously access one base station is decreased.

Since the arrangement shown in FIG. 2A to 2G is employed, sixtime-division multiple access (TDMA) in which six mobile stationsaccesses one band slot is carried out. In view of each of the mobilestations, there is a spare period of two time slots (i.e., 400 μsec.)from completion of reception or transmission of one time slot period tostart of next transmission or reception. Each of the mobile stationscarries out a timing processing and a processing called frequencyhopping by utilizing this spare period. Specifically, each of the mobilestations carries out a timing processing TA for agreeing a transmissiontiming with a timing of a signal transmitted from a base station duringthe period after 200 μsec. have passed before each transmission slot T,and carries out the frequency hopping for switching a band slot used fortransmission and reception to another band slot after about 200 μsec.have passed since completion of each transmission slot T. Since theabove timing is one used when the transmission rate is set high, if thetransmission rate is set low and the number of the band slot to be usedis changed, then it is necessary to set the timing for the frequencyhopping again. The frequency hopping permits a plurality of band slotsprepared for one base station to be used by each of the mobile stationsequally.

Specifically, a plurality of band slots are allocated to a single basestation. In a case of a cellular system in which one base station formsone cell, if a band of 1.2 MHz is allocated to one cell, eight bandslots can be allocated to one cell. Similarly, if a band of 2.4 MHz isallocated to one cell, 16 band slots can be allocated to one cell; if aband of 4.8 MHz is allocated to one cell, 32 band slots can be allocatedto one cell; and if a band of 9.6 MHz is allocated to one cell, 64 bandslots can be allocated to one cell. Then, a frequency switchingprocessing called frequency hopping is carried out so that a pluralityof band slots allocated to one cell are utilized uniformly. In thepresent example, a plurality of band slots of which frequencies arecontinuous are allocated to one cell.

FIGS. 3A and 3B shows an example of a band-slot allocation in whicheight band slots are allocated to one cell. In each of the preparedeight band slots as shown in FIG. 3A, twenty-two carries are set fordata transmission.

The communication condition is settled as above so that a signaltransmitted between each mobile station and the base station ismaintained to have orthogonal properties with respect to other signals.Therefore, the signal will not suffer from interference from othersignals and only a corresponding signal can be extracted satisfactorily.Since a band slot utilized for transmission is changed at any time bythe frequency hopping, the transmission bands prepared for each basestation is effectively utilized, which leads to effective transmission.In this case, as described above, a frequency band to be allocated toone base station (cell) can be freely settled. Therefore, a system canbe freely settled depending on a used situation.

In this embodiment, it is assumed that one-cell repetition system inemploying the same frequency band in all the prepared cells is employed.Specifically, it is assumed that if the eight band slots are prepared asa band which can be used in this radio telephone system as shown inFIGS. 3A and 3B, then all the cells (i.e., all the base stations) carryout communication using the eight band slots.

Next, an arrangement of a terminal apparatus (mobile station) whichcarries out communication with the base station in the above-describedsystem will be described. In this case, a band of 2.0 GHz is utilized asa down-link from the base station to the terminal apparatus while a bandof 2.2 GHz is utilized as an up-link from the terminal apparatus to thebase station.

FIG. 4 is a diagram showing an arrangement of the terminal apparatus. Areception system thereof will be described first. An antenna 11 servingfor transmitting and receiving a signal is connected to an antennasharing device. The antenna sharing device 12 is connected at itsreceived signal output side with a band-pass filter 13, a receptionamplifier 14 and a mixer 15 in series. The band-pass filter 13 extractsa signal of the 2.0 GHz band. The mixer 15 mixes the output from theband-pass filter with a frequency signal of 1.9 GHz output from afrequency synthesizer 31 so that the received signal is converted intoan intermediate frequency signal of a 100 MHz. The frequency synthesizer31 is formed of a PLL (phase-locked-loop circuit), and it is asynthesizer for generating signals in a band of 1.9 GHz with an intervalof 150 kHz (i.e., one band slot interval) based on a signal of 150 kHzwhich is generated by frequency-dividing a signal of 1.9 MHz output froma temperature compensation type crystal oscillator (TCXO) 32 by a 1/128frequency divider 33. Other frequency synthesizers, which will bedescribed later on, utilized in the terminal apparatus are also formedof a PLL circuit.

The intermediate frequency signal output from the mixer 15 is suppliedthrough a band-pass filter 16 and a variable gain amplifier 17 to twomixers 18I, 18Q useful for demodulation. A frequency signal of 100 MHzoutput from a frequency synthesizer 34 is supplied to a phase shifter 35in which the signal is made into two system signals of which phases areshifted from each other by 90 degrees. One of the two-system frequencysignals is supplied to the mixer 18I while the other of the same issupplied to the mixer 18Q so that they are mixed with the intermediatefrequency signal respectively, whereby an I component and a Q componentcontained in the received data are extracted. The frequency synthesizer34 is a synthesizer for generating a signal of 100 MHz band based on thesignal of 150 kHz generated by frequency-dividing of the 1/128frequency-divider 33.

Then, the extracted I-component is supplied through a low-pass filter19I to an analog-to-digital converter 20I in which the component isconverted into digital I data. The extracted Q-component is suppliedthrough a low-pass filter 19Q to an analog-to-digital converter 20Q inwhich the component is converted into digital Q data. In this case, therespective analog-to-digital converters 20I, 20Q use a clock of 200 kHzas a clock for conversion which is generated by dividing a clock of 1.9MHz output from the TCXO 32 by a 1/96 frequency divider 36.

Then, the digital I data and digital Q data output from theanalog-to-digital converters 20I, 20Q are supplied to a demodulatingdecoder 21 in which demodulated reception data is obtained at a terminal22. The demodulating decoder 21 is supplied with the clock of 1.9 MHzoutput from the TCXO 32 as a clock as it is, and also supplied with aclock of 5 kHz generated by frequency-dividing the clock of 200 kHzoutput from the 1/96 frequency divider 36 by a 1/40 frequency-divider37. The clock of 5 kHz is utilized for generating slot timing date.Specifically, in the present example, one time slot is set to 200 μsec.as described above. However, a signal of which frequency is 5 kHz hasone period of 200 μsec. Thus, slot timing data is generated insynchronism with the signal of 5 kHz.

Next, the transmission system of the terminal apparatus will bedescribed. Transmission data obtained at a terminal 41 is supplied to amodulating encoder 42 in which processing for encoding and modulation iscarried out for transmission so as to generate digital I data anddigital Q data for transmission. In this case, the modulating encoder 42is supplied with the clock of 1.9 MHz as a clock which is output fromthe TCXO 32 as it is, and also supplied with the signal of 5 kHzgenerated by division with the 1/40 frequency-divider 37 as data forgenerating a slot timing. The digital I data and the digital Q dataoutput from the modulating encoder 42 are supplied to digital-to-analogconverters 43I and 43Q in which the data are converted into an analog Isignal and an analog Q signal. The converted I signal and Q signal aresupplied through low-pass filters 44I and 44Q to mixers 45I and 45Q.Further, a frequency signal of 300 MHz output from a frequencysynthesizer 38 is converted by a phase shifter 39 into two systemsignals of which phases are shifted from each other by 90 degrees. Oneof the two system frequency signals is supplied to the mixer 45I whilethe other of the same is supplied to the mixer 45Q, whereby thefrequency signals are mixed with the I signal and the Q signal,respectively, so as to form signals falling in a 300 MHz band. Both ofthe signals are supplied to an adder 46 in which carried out is anorthogonal modulation to unify them into a single system signal. Thefrequency synthesizer 38 is a synthesizer for generating a signal of 300MHz band based on the signal of 150 kHz generated by afrequency-division with the 1/128 frequency-divider 33.

Then, the signal modulated into the signal of 300 MHz band output fromthe adder 46 is supplied through a transmission amplifier 47 and aband-pass filter 48 to a mixer 49, in which the signal is added with afrequency signal of 1.9 GHz output from the frequency synthesizer 31 soas to convert the signal into a signal of a transmission frequency of2.2 GHz band. The transmission signal frequency-converted into thetransmission frequency is supplied through a transmission amplifier(variable gain amplifier) 50 and a band-pass filter 51 to the antennasharing device 12 so that the signal is transmitted from the antenna 11connected to the antenna sharing device 12 in a wireless fashion. A gainof the transmission amplifier 50 is controlled to thereby adjust atransmission output. The control in transmission output is carried outbased on output control data received from the base station side, forexample.

Further, the signal of 19.2 MHz output from the TCXO 32 is supplied to a1/2400 frequency-divider 40 to be converted into a signal of 8 kHz, andthe signal of 8 kHz is supplied to a circuit of a speech processingsystem (not shown). That is, in the terminal apparatus of the presentexample, a speech signal transmitted between it and the base station issampled at a rate of 8 kHz (or oversampling at a rate of an integralmultiple of the frequency). Thus, the 1/2400 frequency divider 40produces a clock necessary for speech data processing circuits such asan analog-to-digital converter and a digital-to-analog converter of aspeech signal or a digital signal processor (DSP) processing compressionand expansion on speech data and so on.

Next, the encoder in the transmission system of the terminal apparatusof the arrangement and its peripheral arrangement will be described indetail with reference to FIG. 5. A convolution encoder 101 subjects atransmission data to convolution encoding. The convolution encoding iscarried out with a constrained length of k=7 and a coding rate of R=1/3,for example. FIG. 6 is a diagram showing an arrangement of theconvolution encoder with a constrained length of k=7 and a coding rateof R=1/3. Input data is supplied to six delay circuits 101a, 101b, . . ., 101f which are connected in series so that data of continuous 7 bitsare made coincident in their timing. Ex-OR gate 101g, 101h, 101i take anexclusive-OR of a predetermined data of the seven bits and outputs ofthe respective Ex-OR gates 101g, 101h, 101i are converted into paralleldata by a serial-to-parallel converting circuit 101j, wherebyconvolution-encoded data is obtained.

FIG. 5 is again described. An output of the convolution encoder 101 issupplied to a four-frame interleave buffer 102 in which data interleaveis carried out over four frames (20 msec.). An output of the interleavebuffer 102 is supplied to a DQPSK encoder 110 in which a DQPSKmodulation is carried out. That is, a DQPSK symbol generating circuit111 generates a corresponding symbol based on supplied data, and thenthe symbol is supplied to a multiplier 112 at one input terminalthereof. A delay circuit 113 delays a multiplied output of themultiplier 112 by one symbol amount and returns it to the other inputterminal thereof, whereby the DQPSK modulation is carried out. The DQPSKmodulated data is supplied to a multiplier 103 so that random phaseshift data output from a random phase shift data generating circuit 104is multiplied with the modulated data, whereby phase of the data isapparently changed at random.

An output of the multiplier 103 is supplied to an inverse fast Fouriertransformation (IFFT) circuit 105 in which a conversion processing to atime axis is carried out on the data of the frequency axis bycalculation of the inverse fast Fourier transformation, whereby data onthe real time axis of the multicarrier signal of 22 subcarriers with aninterval of 6.25 kHz is produced. The IFFT circuit 105 for carrying outthe inverse fast Fourier transformation enables an arrangement forgenerating subcarriers of a second powered number relatively easily. TheIFFT circuit 105 employed in the present example is capable ofgenerating 2⁵ subcarriers, i.e., 32 subcarriers and outputs datamodulated into continuous 22 subcarriers of the generated subcarriers.The modulation rate of transmission data dealt by the FFT circuit 105 ofthe present example is set to 200 kHz. A signal of a modulation rate of200 kHz is converted into thirty-two multicarriers to producemulticarrier signals with an interval of 6.25 kHz, which numeral derivesfrom calculation of 200 kHz÷32=6.25 kHz.

The multicarrier data transformed into data of the real time by theinverse fast Fourier transformation is supplied to a multiplier 107 inwhich the data is multiplied with a time waveform output from awindowing data generating circuit 106. The time waveform is a waveformhaving one waveform length T_(u), or about 200 μsec. (that is, one timeslot period) as shown in FIG. 7A, for example, on the transmission side.However, the waveform is arranged to have its both end portions T_(TR)(about 15 μsec.) changing gently in its waveform level. Hence, theneighboring time waveforms are arranged to overlap partly on each otheras shown at FIG. 7B when the time waveform is utilized formultiplication.

FIG. 5 is again described. The signal multiplied with the time waveformby the multiplier 107 is supplied through a burst buffer 108 to an adder109. The adder 109 adds control data output from a control data selector121 to the signal at a predetermined position. The control data utilizedfor addition is control data indicating control of transmission output.Based on a result of determination over the condition of the receivedsignal at a terminal 122, the selector 121 sets the control data.

In this case, the selector 121 is connected with three control datamemories 123, 124, 125 (actually, these memories may be provided bydividing an area of one memory into three portions). Control data fordecreasing a transmission output (-1 data) is stored in the memory 123,control data for keeping the transmission output in an unchanged state(±0 data) is stored in the memory 124, and control data for increasingthe transmission output (+1 data) is stored in the memory 125,respectively. The control data stored in this case is data equivalent todata when the corresponding control data is subjected to the modulationprocessing for transmission in the encoder up to the multiplier 107.

More concretely, the transmission data is a phase-modulated datachanging on a plane formed by the I-axis and the Q-axis orthogonal toeach other, i.e., the data changing along a circle on a plane shown inFIG. 8. Data (I, Q) at a position of (0, 0) is set to ±0 data, that at aposition of (1, 0) behind from the position by 90 degrees is set to -1data and that at a position of (0, 1) ahead of the position of ±0 databy 90 degrees is set to +1 data. Control data for the transmissionoutput corresponding to a position of (1, 1) is undefined so that whenthe reception side discriminates the data of the position, the data isregarded as ±0 data to keep the transmission output unchanged. Thesignal phase shown in FIG. 8 is a phase before being modulated intomulticarrier signals. Actually, the data of the signal phase ismodulated into multicarrier signal and data generated by multiplied witha time waveform are stored in respective memories 123, 124, 125.

Transmission data added with the control data by the adder 109 issupplied to a digital-to-analog converter 43 (which corresponds to thedigital-to-analog converters 43I, 43Q shown in FIG. 4) in which thetransmission data is converted into an analog signal using a clock of200 kHz for conversion.

Next, the decoder and the peripheral arrangement thereof of thereception system of the terminal apparatus of the present example willbe described in detail with reference to FIG. 9. Digital data resultingfrom conversion by an analog-to-digital converter 20 (corresponding tothe analog-to-digital converters 20I, 20Q in FIG. 4) using a clock of200 kHz, is supplied through a burst buffer 131 to a multiplier 132, inwhich the digital data is multiplied with a time waveform output from aninverse windowing data generating circuit 133. The time waveformutilized for multiplication upon reception is a time waveform with ashape shown in FIG. 7A. This time waveform is arranged to have a length,T_(M), i.e., 160 μsec. which is shorter than the length of the same upontransmission.

The reception data multiplied with the time waveform is supplied to aFFT circuit 134 in which conversion between a frequency axis and atimebase is carried out by the fast Fourier transformation processing,whereby the transmitted data modulated into 22 subcarriers with aninterval of 6.25 kHz and arranged on the time base are separated intoinformation component which each carrier has. The conversion processingin this case is carried out by a circuit capable of processingsubcarriers of 2⁵, i.e., thirty-two subcarriers, similarly to the casein which conversion processing is carried out by the IFFT circuit in thetransmission system. Data modulated into continuous twenty-twosubcarriers of them are converted and output therefrom. The modulationrate of transmission data dealt by the FFT circuit 134 of the presentexample is set to 200 kHz. Since the circuit is capable of processingthirty-two multicarriers, conversion processing can be carried out onmulticarriers with an interval of 6.25 kHz, which numeral derives fromcalculation of 200 kHz÷32=6.25 kHz.

The reception data which has been subjected to the fast Fouriertransformation in the FFT circuit 134 is supplied to a multiplier 135,in which the reception data is multiplied with inverse random phaseshift data (this data is data changing in synchronism with random phaseshift data on the transmission side) output from an inverse random phaseshift data generating circuit 136, whereby the data is restored to haveits original phase.

The data restored to have its original phase is supplied to adifferential demodulation circuit 137 in which the data is subjected todifferential demodulation. The differentially demodulated data issupplied to a four-frame deinterleave buffer 138 in which datainterleaved over four frames upon transmission is restored to have itsoriginal data order. The deinterleaved data is supplied to a Viterbidecoder 139 in which the data is Viterbi-decoded. The Viterbi-decodeddata is supplied as decoded reception data to a reception dataprocessing circuit (not shown) placed in the later stage.

FIG. 10 shows timings of processings described so far. Initially, dataof one time slot is received at timing R11 in the reception system, andsimultaneously with the reception, the received data is converted intodigital data by the analog-to-digital converter 20 and then stored inthe burst buffer 131. The stored reception data is subjected todemodulation processings such as multiplication with the time waveform,the fast Fourier transform, multiplication with the inverse random phaseshift data, differential demodulation, Viterbi demodulation and so on atthe next timing R12. Thereafter, decoding is carried out by dataprocessing at the next timing R13.

Then, from timing R21 which is six time slots after timing R11, totiming R23, a processing the same as that of timing R11 to R13 iscarried out. Thereafter, the same processing is repeated.

In the transmission system, transmission is carried out at a timingshifted by three time slots with respect to the timing of reception.That is, the transmission data is encoded at predetermined timing T11,the encoded data is subjected to a modulation processing by which thedata is converted into transmission data of one burst amount at the nexttiming T12, and the data is once stored in the burst buffer 108 of thetransmission system. Then, at timing T13 behind three time slots fromthe reception timing R11, the transmission data stored in the burstbuffer 108 is converted by the digital-to-analog converter 43 and thensubjected to transmission processing and transmitted from the antenna11. Then, from timing T21, which is six time slots after timing Y11, totiming T23 a processing the same as that of timing T11 to T13 is carriedout. Thereafter, the same processing is repeated.

In this way, reception processing and transmission processing arecarried out intermittently in a time sharing manner. In the presentexample, control data (control bit) of the transmission output to beadded to transmission data is, i.e., the control data of thetransmission output upon transmission as described with reference toFIG. 5 is, added by the adder 109 at the last timing when the encodeprocessing is completed for transmission. Therefore, the state of thereception data can be swiftly reflected upon the control data to betransmitted. That is, for example, reception state of the burst signalreceived at timing R11 is detected at a midst of demodulation at timingR12, and the control state of the transmission output to be notified tothe opponent of communication (base station) is determined (i.e., FIG.10 shows a processing at a timing indicating control bit calculation).When the control bit is calculated, the result of calculation is sentfrom the terminal 122 to the selector 121, in which the calculationresult is added with control data corresponding to transmission datastored in the burst buffer 108, and a burst signal to be transmitted attiming T13 is added with control data of transmission output based onthe last received data indicative of the state.

The opponent carrying out communication (base station) determines thecontrol data transmitted at timing T13 so that the opponent controls thetransmission output into the corresponding state when the burst signalis transmitted from the base station at the next timing R21.Consequently, the burst signal to be transmitted next is controlled inits transmission output on the basis of the reception state of the burstsignal which has been transmitted in the preceding cycle. Thus, thetransmission output is positively controlled at every one cycle when theburst signal is transmitted, and hence it is possible to substantiallyuniform transmission outputs of transmission signals transmitted througha plurality of paths between the terminal apparatus and one base stationat the same time.

If it is not carried out the processing that, as in the present example,the control data of the transmission output is prepared in the memory inadvance to carry out adding processing, then the following consequencewill happen in the example of FIG. 10, for example. That is, a resultreceived at timing R11 is determined in the process of demodulation attiming R12, thereafter the control data is encoded at timing T21 anddemodulated at timing T22, and the control data based on the receptionresult at timing R11 is transmitted in response to the burst signaltransmitted at timing T23. Thus, it is impossible to control thetransmission output at every cycle. While description has been made on acase in which the terminal apparatus side generates data useful forcontrolling the transmission output from the base station, it isneedless to say that the base station side may also generate data usefulfor controlling the transmission output from the terminal apparatus.

In the terminal apparatus according to this embodiment, the low-speedtransmission rate can be set other than the transmission rate obtainedupon the operation with the clocks of the above respective frequencies.If the transmission rate is set to the low-speed transmission rate, amodulation clock frequency, a demodulation clock frequency and so on arechanged in accordance with the setting. The transmission rate is setbased on a command from a control unit, not shown, of the terminalapparatus. This control unit sets either of a normal (high speed)transmission rate and the low-speed transmission rate based on a setdata of the transmission rate transmitted from the base station.

An arrangement of the base station will be described below withreference to FIG. 11. The arrangement of the base station for carryingout transmission and reception is fundamentally the same as thearrangement of the terminal apparatus side. But the base station isdifferent from the terminal apparatus in an arrangement of multipleaccess which enables a plurality of terminal apparatus to access at atime.

Initially, an arrangement of the reception system shown in FIG. 11 willbe described. An antenna 211 serving for transmission and reception isconnected to an antenna sharing device 212. The antenna sharing device212 is connected at its reception signal output side with a band-passfilter 213, a reception amplifier 214 and a mixer 215 in series. Thebandpass filter 213 extracts 2.2 GHz band. The mixer 215 mixes anextracted signal with a frequency signal of 1.9 GHz output from afrequency synthesizer 231 so that a reception signal is converted intoan intermediate signal of 300 MHz band. The frequency synthesizer 231 isformed of a PLL circuit (phase-locked loop circuit). The frequencysynthesizer is a synthesizer for generating signals of 1.9 GHz with aninterval of 150 kHz (i.e., one band slot interval) on the basis of asignal of 150 kHz generated by frequency-dividing a signal of 1.9 MHzoutput from a temperature-compensated crystal oscillator (TCXO) 232 by a1/128 frequency divider 233. Other synthesizers, which will be describedlater on, utilized in the base station are similarly formed of the PLLcircuit.

The intermediate frequency signal output from the mixer 215 is suppliedthrough a band-pass filter 216 and a reception amplifier 217 to twomixers 218I, 218Q useful for demodulation. A frequency signal of 300 MHzoutput from a frequency synthesizer 234 is converted into signals of twosystems of which phases are shifted from each other by 90 degrees by aphase shifter 235. One of the two system frequency signals is suppliedto the mixer 218I while the other of the same is supplied to the mixer218Q so that they are mixed with the intermediate frequency signals,respectively. Thus, an I-component and a Q-component contained in thereceived data are extracted. The frequency synthesizer 234 is asynthesizer for generating a signal of 300 MHz band on the basis of asignal of 150 kHz generated by the frequency division with the 1/128frequency divider 233.

The extracted I-component is supplied through a low-pass filter 219I toan analog-to-digital converter 220I in which the component is convertedinto digital I data. The extracted Q-component is supplied through alow-pass filter 219Q to an analog-to-digital converter 220Q in which thecomponent is converted into digital Q data. Each of theanalog-to-digital converters 220I, 220Q utilizes a signal of 6.4 MHzgenerated by frequency-dividing a signal of 1.9 MHz output from the TCXO232 by a 1/3 frequency divider 236 as a clock for conversion.

Then, the digital I data and the digital Q data output from theanalog-to-digital converters 220I, 220Q are supplied to a demodulatingunit 221 from which demodulated data is supplied to a demultiplexer 222,in which the data supplied thereto is classified into data fromrespective terminal apparatus and the classified data are suppliedseparately to decoders 223a, 223b, . . . , 223n of which numbercorresponds to a number of terminal apparatus permitted to access at atime (six terminals per one band slot). The demodulating unit 221, thedemultiplexer 222 and the decoders 223a, 223b, . . . , 223n are suppliedwith the signal of 1.9 MHz output from the TCXO 32 as a clock as it is,and also supplied with a signal of 5 kHz generated by frequency-dividinga signal of 6,4 MHz output from the 1/3 frequency divider 236 by afrequency divider 237 as slot timing data.

Next, an arrangement of a transmission system of the base station willbe described. A multiplexer 242 synthesizes transmission data which areseparately encoded by encoders 241a, 241b, . . . , 241n prepared forrespective opponents (terminal apparatus) capable of communicating at atime. An output of the multiplexer 242 is supplied to a modulation unit243 in which modulation processing for transmission is carried out,whereby digital I data and digital Q data for transmission aregenerated. The respective encoders 241a to 241n, the multiplexer 242 andthe modulation unit 243 are directly supplied with the signal of 1.9 MHzoutput from the TCXO 32 as a clock as it is, and also supplied with thesignal of 5 kHz output from the 1/1280 frequency divider 237 as a clock.

The digital I data and the digital Q data output from the modulationunit 243 are supplied to digital-to-analog converters 244I and 244Q inwhich the digital data are converted into an analog I signal and ananalog Q signal. The converted I signal and Q signal are suppliedthrough low-pass filters 245I and 245Q to mixers 246I and 246Q. Further,a frequency signal of 100 MHz output from a frequency synthesizer 238 isconverted by a phase shifter 239 into two system signals of which phasesare shifted from each other by 90 degrees. One of the two systemfrequency signals is supplied to the mixer 246I while the other of thesame is supplied to the mixer 246Q, whereby the frequency signals aremixed with the I signal and the Q signal, respectively, so as to formsignals falling in a 300 MHz band. Both of the signals are supplied toan adder 247 in which carried out is an orthogonal modulation to unifythem into a single system signal. The frequency synthesizer 238 is asynthesizer for generating a signal of 100 MHz band based on the signalof 150 kHz generated by a frequency-division with a 1/128frequency-divider 233.

Then, the signal modulated into the signal of 100 MHz band output fromthe adder 247 is supplied through a transmission amplifier 248 and aband-pass filter 249 to a mixer 250, in which the signal is added with afrequency signal of 1.9 GHz band output from the frequency synthesizer231 so as to convert the signal into a signal of a transmissionfrequency of 2.0 GHz band. The transmission signal frequency-convertedinto the transmission frequency is supplied through a transmissionamplifier 251 and a band-pass filter 252 to the antenna sharing device212 so that the signal is transmitted from the antenna 211 connected tothe antenna sharing device 212 in a wireless fashion.

Further, the signal of 1.9 MHz output from the TCXO 232 is supplied to a1/2400 frequency-divider 240 to convert the signal into a signal of 8kHz, and the signal of 8 kHz is supplied to a circuit of a speechprocessing system (not shown). That is, the base station of the presentexample is arranged to sample a speech signal, which is transmittedbetween the terminal apparatus and a base station, at a rate of 8 kHz(or oversampling at a rate of an integral multiple of the rate), andthus the 1/2400 frequency divider 240 produces a clock necessary forspeech data processing circuits such as an analog-to-digital converterand a digital-to-analog converter of a speech signal or a digital signalprocessor (DSP) for processing for compression and expansion on speechdata and so on.

Next, an arrangement of the base station for encoding and modulatingtransmission data will be described in detail with reference to FIG. 12.In this case, it is supposed that N (N is an arbitrary number) terminalapparatus (users) carry out multiple access at a time. Thus, convolutionencoders 311a, 311b, . . . , 311n subjects transmission signals U0, U1,. . . , UN to respective users of the terminal apparatus to convolutionencoding, respectively. The convolution encoding is carried out with aconstraint length k=7 and a coding rate R=1/3, for example.

Then, data convolution-encoded by respective systems are supplied tofour-frame interleave buffers 312a, 312b, . . . , 312n, respectively, ineach of which interleave is carried out on data over four frames (20msec.). Outputs of respective interleave buffers 312a, 312b, . . . ,312n are supplied to DQPSK encoders 320a, 320b, . . . , 320n,respectively, in each of which DQPSK modulation is carried out.Specifically, DQPSK symbol generating circuits 321a, 321b, . . . , 321ngenerate corresponding symbols based on the supplied data. The symbolsare supplied to one input of multipliers 322a, 322b, . . . , 322n, andmultiplied outputs of the multipliers 322a, 322b, . . . , 322n aresupplied to respective delay circuits 323a, 323b, . . . , 323n in eachof which the symbol is delayed by one symbol amount and fed back to theother input. Thus, DQPSK modulation is carried out. Then, the datasubjected to the DQPSK modulation are supplied to the multipliers 313a,313b, . . . , 313n, respectively, in which random phase shift dataseparately output from random phase shift data generating circuit 314a,314b, . . . , 314n are multiplied with modulation data. Thus, Respectivedata are changed in phase at random apparently.

Outputs of the respective multipliers 313a, 313b, . . . , 313n aresupplied to other multipliers 315a, 315b, . . . , 315n in each of whichthe output are multiplied with control data output from transmissionpower control circuits 316a, 316b, . . . , 316n provided at everysystem. Thus, the transmission output is adjusted. This adjustment oftransmission output is carried out base on output control data containedin the burst signal transmitted from a terminal apparatus connected toeach system. The control data has been described in detail withreference to FIG. 10. That is, if control data of (0, 0) and (1, 1) of(I, Q) data are discriminated from reception data, then the transmissionoutput is maintained as it is, if control data of (0, 1) isdiscriminated from the reception data, then the transmission output isincreased, and if control data of (1, 0) is discriminated from thereception data, then the transmission output is lowered.

The control data of (1, 1) is data which is not actually present on thetransmission side. However, when the data of (1, 1) is determined on thereception side, the output is prevented from being changed. Owing to thesetting, if the control data of (1, 0) (i.e., data making the output tobe lowered) is deviated in phase by 90 degrees due to any cause, anderroneously determined as data of (1, 1) or (0, 0) on the receptionside, then it is possible to avoid at least an erroneous processing inthe inverse direction which increases the output. Similarly, if thecontrol data of (0, 1) (i.e., data making the output to be increased) isdeviated in phase by 90 degrees due to any cause, and erroneouslydetermined as data of (1, 1) or (0, 0) on the reception side, then it ispossible to avoid at least an erroneous processing of the output.

The arrangement shown in FIG. 12 will be described again. Thetransmission data output from the respective multipliers 315a, 315b, . .. , 315n are supplied to a multiplexer 242 and then synthesized thereby.When the transmission data are synthesized by the multiplexer 242according to this embodiment, a frequency at which the transmission dataare synthesized can be switched by a unit of 150 kHz. By the switchingcontrol, the frequency of the burst signal supplied to each terminalapparatus is switched. Specifically, in this embodiment, as describedwith reference to FIGS. 2A to 2G and so on, an operation of switching afrequency by a band slot unit which is called a frequency hopping iscarried out, and the frequency switching operation is realized byswitching processings of the multiplexer 242 upon the synthesizingoperation.

The data synthesized by the multiplexer 242 is supplied to an IFFTcircuit 332 which carries out the inverse fast Fourier transform for thedata, and then obtains a so-called multi-carrier data modulated so as tohave twenty two subcarriers having frequencies at every 6.25 kHz per oneband slot and converted into the real time. Then, the data convertedinto the real time signal by the inverse fast Fourier transform issupplied to a multiplier 333 which multiplies it with a time waveformoutput from a windowing data generating circuit 334. As shown in FIG.7A, for example, the time wave form is a waveform whose length T_(U) ofone waveform is about 200 μsecond (i.e., one time slot period). However,at each of its both end portions T_(TR) thereof (about 15 μsecond), alevel of the waveform is smoothly changed. When the waveform ismultiplied with the time wave form as shown in FIG. 7B, adjacent timewaveforms are partially overlapped with each other.

Then, the signal multiplied with the time waveform by the multiplier 333is supplied through a burst buffer 335 to a digital/analog converter 244(corresponding to the converters 244I, 244Q shown in FIG. 11) whichconverts it into an analog I signal and an analog Q signal. Then, theanalog signals are processed for transmission in the arrangement shownin FIG. 11.

In the base station according to this embodiment, since the band slotswitching processing called frequency hopping is carried out by themultiplexer 242 in the middle of the modulation processing as describedabove, it is possible to simplify the arrangement of the transmissionsystem. Specifically, when the base station simultaneously handles aplurality of paths of signals as described in this embodiment, it wasnecessary to convert a frequency of a signal of each of paths into thatof a corresponding band slot (channel) to then synthesize the signals,and hence, in the transmission system, a set of the circuits up to themixer 250 shown in FIG. 11 is required as much as the paths. On theother hand, in the base station of this embodiment, only one system ofthe circuits is sufficient in the circuits succeeding the multiplexer242, and hence the arrangement of the base station can be simplified tothat extent.

An arrangement for demodulating received data in the base station todecode it will be described in detail with reference to FIG. 13. Adigital I data and a digital Q data converted by an analog/digitalconverter 220 (corresponding to the analog/digital converters 220I and220Q in FIG. 11) are supplied through a burst buffer 341 to a multiplier342. The multiplier multiplies them with a time waveform output from aninverse windowing data generating circuit 343. The time waveform is atime waveform having a shape shown in FIGS. 7A and 7B and also a timewaveform having a length T_(M) of 160 μsec which is shorter than thatused upon transmission.

The received data multiplied with the time waveform is supplied to a FFTcircuit 344 and subjected to fast Fourier transform thereby carrying outa processing of converting a frequency axis into a time axis. Thus, eachof the data transmitted after modulation in the form of 22 subcarriersat an interval of 6.25 kHz per one band slot is obtained from the realtime signal. Then, the data subjected to the fast Fourier transform issupplied to a demultiplexer 222 and divided into data which is as muchas the terminal apparatus permits in multiple access to the base stationsimultaneously. When the data is divided by the demultiplexer 222according to this embodiment, the frequency used for the above divisionis switched by a unit of 150 kHz and this switching operation iscontrolled, thereby frequencies of the burst signals transmitted fromthe respective terminal apparatus are switched. Specifically, in thisembodiment, as described with reference to FIG. 1 and so on, theoperation of switching the frequency of a band slot unit which is calledfrequency hopping is carried out periodically, and the frequencyswitching operation carried out on the reception side is realized bytime-dividing processings of the demultiplexer 222 upon reception of thereceived data.

The respective received data divided by the demultiplexer 222 areindependently supplied to multiplexers 351a, 351b, . . . , 351n providedso as to be as much as the terminal apparatus of the number N permittedin simultaneous multiple access to the base station. The multipliers351a, 351b, . . . , 351n respectively multiply the divided data withinverse random phase shift data (data changed in synchronization withthe random phase shift data on the transmission side) output from theinverse random phase shift data generating circuits 352a, 352b, . . . ,352n and returns the received divided data to the data having theoriginal phases in the respective systems.

The respective data from the inverse random phase shift data generatingcircuits are supplied to delay detection circuits 353a, 353b, . . . ,353n and delay-detected (differentially demodulated) thereby. The delaydetection circuits supplies the delay detected data to four-frameinterleave buffers 354a, 354b, . . . , 354n which restore the data offour frames interleaved upon transmission to the data of the originaldata arrangement. The four-frame interleave buffers supply thede-interleaved data to Viterbi decoders 355a, 355b, . . . , 355n forsubjecting them to Viterbi decoding. The decoders supply the datasubjected to the Viterbi decoding as the received data to received-dataprocessing circuits (not shown) at the succeeding stages.

According to the base station of this embodiment, since the datadividing processing including the band slot switching processing calledthe frequency hopping is carried out by the demultiplexer 222 providedin the middle of the demodulation processing, similarly to thetransmission system, it is possible to simplify the arrangement of thereception system. Specifically, when the base station simultaneouslyhandles the signals of plural paths as described in this embodiment, itis necessary in the prior art to convert the frequencies of the signalsof the band slots (channels) corresponding to the respective signals ofpaths into the intermediate frequency signals and then to carry out theprocessings up to the fast Fourier transform to supply them to therespective multipliers 351a to 351n, and hence in the reception system,sets, which are as much as the number of the paths, of the circuits fromthe mixer 215 to the demodulating unit 221 shown in FIG. 11 arerequired. On the other hand, since the base station according to thisembodiment requires only one system of circuits in the transmissionsystem preceding to the demultiplexer 222, it is possible to simplifythe arrangement of the base station to that extent.

In this base station, similarly to the terminal apparatus, the low-speedtransmission rate can be set other than the transmission rate obtainedupon the operation with the clocks of the above respective frequencies.If the transmission rate is set to the low-speed transmission rate, amodulation clock frequency, a demodulation clock frequency and so on arechanged in accordance with the setting. The transmission rate is setbased on a command from a control unit, not shown, of the terminalapparatus. This control unit sets either of a normal (high speed)transmission rate and the low-speed transmission rate based on a setdata of the transmission rate transmitted from the base station.

A processing for setting the transmission rate according to thisembodiment will be described with reference to FIG. 14 by way ofexample. For example, it is assumed that a certain terminal apparatus(mobile station) MS is kept in a state that it can communicate with abase station A forming an area (cell) A₀. It is assumed that thecommunication between the base station A and the terminal apparatus MSis started from call-out from the terminal apparatus MS or call-in tothe terminal apparatus MS. At this time, initially, the transmissionrate is set low under the control of the base station A. The reason forsetting the transmission rate to the low-speed one upon the initialaccess is that interference given to another station is unknown uponstart of communication.

In a state that the low-speed transmission rate is set, a base station Bin an adjacent area B₀ measures an interference power given to theadjacent base station B because of the communication between the basestation A and the terminal apparatus MS. If it is determined that theinterference is a large one having a predetermined level or larger basedon the measurement, then the base station B informs the base station Aof this determination through communication employing a groundcommunication path C between the base station B and the base station A.If no data indicating that the communication interferes largely withother base station adjacent to the area A₀ is not transmitted from allof the base stations adjacent to the area A₀, then it is determined thatthe communication condition is satisfactory. The transmission rate ofthe communication between the base station A and the terminal apparatusMS is changed to the high transmission rate (i.e., the normaltransmission rate).

The base station of each cell always measures the interference powergiven by communication in other cell at any time as well as the start ofthe communication. If detecting the interference power of apredetermined level or larger, the base station informs the base stationcarrying out the communication serving as a source of interference ofdetection of the large interference power by using the groundcommunication path C. The base station received such informationcontrols the transmission rate of the communication serving as theinterference source to be lowered.

In particular, according to this embodiment, since the same frequencyband is used in each of the areas (cells), as shown in FIG. 14, if theterminal apparatus MS is located in the vicinity of the boundary portionbetween the adjacent areas, then the interference power given to otherstation is large. If it is determined that the communication is carriedout in the vicinity of the boundary portion between the adjacent areasin consideration of the intensity of the interference power, then theprocessing for lowering the transmission rate is carried out. When thecommunication is carried out in the vicinity of the boundary portionbetween the adjacent areas as described above, if the terminal apparatusMS is moved to another position and consequently a hand-off processingfor switching a base station communicating with the terminal apparatusMS from the base station A to the base station B is carried out, thehand-off processing is carried out in a state that the communicationwith low transmission rate is carried out, which can reduce thepossibility of failure of the hand-off processing.

Since, when the communication interferes with the adjacent cell largely,the transmission rate is lowered to carry out the communication, as thetransmission rate is lowered, the amount of the data to be transmittedis lowered and hence the interference given to the adjacent cell islowered. Therefore, it is possible to effectively reduce theinterference given to the adjacent cell when the one-cell repetitionsystem is employed in a cell arrangement.

While in this embodiment the base station in the adjacent measures theinterference power to measure the amount of the interference anddetermines whether or not the transmission rate is to be changed, thepresent invention is not limited thereto. The terminal apparatus MS maymeasure a power of a signal transmitted from the adjacent base station Band then determine the interference power thereof to transmit themeasurement result to the base station A communicating therewith as thecontrol data to reduce the transmission rate under the control of thebase station A. In this arrangement, it is possible to change thetransmission rate without the data of the interference power transmittedfrom the base station in the adjacent cell.

While the transmission rate is changed at two steps in this embodiment,the present invention is not limited thereto and the transmission ratemay be changed at more steps. Moreover, while in this embodiment thetransmission rate is changed by changing the number of the time slots tobe used, the present invention is not limited thereto and otherprocessing may be employed to change the transmission rate.

While in this embodiment the BDMA system is employed as thecommunication system, the present invention is not limited thereto andcan be applied to any communication system as long as the one-cellrepetition system can be applied to the communication system. Forexample, when the one-cell repetition system is applied to a cellularsystem of the code-division multiple access (CDMA) system, if theinterference power is at a predetermined level or higher, then thetransmission rate may be lowered upon the commencement of the access.

Moreover, values of the frequencies, time, coding rates and so on aredescribed in this embodiment by way of example, and hence the presentinvention is not limited to the above embodiment. It is needless to saythat the present invention can be applied to the modulation processingother than the DQPSK modulation in view of the modulation system.

According to the present invention, when there is possibility that theinterference given to the another cell is large, it is possible to carryout the communication with the interference being suppressed to aminimum. Therefore, it is possible to constantly carry out thecommunication employing the one-cell repetition system satisfactorily.

In this case, the following communication system is employed; aplurality of transmission bands in each of which subcarrier signals of apredetermined number are disposed at a predetermined frequency intervalare prepared, a signal in each of the transmission bands is divided byevery predetermined time to form time slots, and a burst signal istransmitted in the form of a multicarrier signal modulated by dispersingthe signal intermittently into the subcarrier signals of the abovepredetermined number at a period of the time slots of a predeterminednumber. Therefore, it is possible to satisfactorily carry out thecommunication employing the one-cell repetition system to which theabove communication system is applied, without interfering with thecommunication of another cell.

Since the code-division multiple access system is employed as thecommunication system used between the base station and the terminalapparatus, it is possible to satisfactorily carry out the communicationemploying the one-cell repetition system to which the abovecommunication system is applied, without interfering with thecommunication of another cell.

Having described preferred embodiments of the present invention withreference to the accompanying drawings, it is to be understood that thepresent invention is not limited to the above-mentioned embodiments andthat various changes and modifications can be effected therein by oneskilled in the art without departing from the spirit or scope of thepresent invention as defined in the appended claims.

What is claimed is:
 1. A communication method in a predeterminedbandwidth with a predetermined format for multiple access by each cell,comprising the steps of:detecting an interference by a base station ofanother cell of a communication between a first apparatus and a secondapparatus; sending one of an information that said interference isdetected in said detecting step and an information that existence ofsaid interference is unknown to said first or said second apparatus,wherein a processing in said sending step is carried out through a radiocommunication among a plurality of base stations; and lowering aninformation transmission rate of said communication between said firstand said second apparatus in response to said information sent by saidstep of sending.
 2. The communication method according to claim 1,wherein a common frequency band for communication is employed in a cellwhere said first apparatus belongs and a cell where said third apparatusbelongs.
 3. The communication method according to claim 2, wherein saidpredetermined format employs a multicarrier signal formed by a unitwhich includes subcarriers of a predetermined number and time slots ofsaid predetermined number.
 4. The communication method according toclaim 2, wherein said predetermined format is a code division multipleaccess format.
 5. The communication method according to claim 1, whereinsaid predetermined format employs a multicarrier signal formed by a unitwhich includes subcarriers of a predetermined number and time slots ofsaid predetermined number.
 6. The communication method according toclaim 4, wherein said predetermined format is a code division multipleaccess format.
 7. The communication method according to claim 1, whereina processing in said lowering step is carried out by lowering saidinformation transmission rate in a communication path between said firstand said second apparatus without varying a capacity of saidcommunication path.
 8. The communication method according to claim 1,wherein a processing in said lowering step is carried out by loweringsaid information transmission rate per unit of communication pathbetween said first and said second apparatus while increasing a capacityof said path.
 9. The communication method according to claim 1, whereina processing in said lowering step is carried out by lowering saidinformation transmission rate per unit of communication path betweensaid first and said second apparatus while increasing a capacity of saidpath.
 10. A communication method in a predetermined bandwidth with apredetermined format for multiple access by each cell, comprising thesteps of:detecting an interference by a second base station when a firstbase station is communicating with a subscriber in a cell, where saidfirst base station is located and said subscriber is located at an edgeof said cell and is approaching a cell where said second base station islocated; and lowering an information transmission rate of saidcommunication between said first base station and said subscriber inresponse to information detected from said step of detecting, whereinsaid information is sent by said second base station to one of saidfirst base station and said subscriber.
 11. The communication methodaccording to claim 10, wherein a common frequency band for communicationis employed in a cell where said first base station belongs and a cellwhere said second base station belongs.
 12. The communication methodaccording to claim 10, wherein a processing in said lowering step iscarried out by lowering said information transmission rate in acommunication path between said first and said second apparatus withoutvarying a capacity of said communication path.
 13. A communicationapparatus for communicating in a predetermined bandwith with apredetermined format for multiple access by each cell,comprising:communicating means for communicating with a predeterminedstation; information receiving means for receiving a predeterminedcommunication status information from a third station; and rateadjusting means for lowering an information transmission rate of saidcommunication apparatus and said predetermined station when an outputsignal from said information receiving means indicates that saidcommunication status of said third station is one of a status having alevel lower than a predetermined value and an unknown status.
 14. Thecommunication apparatus according to claim 13, wherein said thirdstation is a base station of another cell, and said communication statusinformation is transmitted by wire communication.
 15. The communicationapparatus according to claim 13, wherein a common frequency band forcommunication is employed in a cell where said predetermined stationbelongs and a cell where said third station belongs.
 16. Thecommunication apparatus according to claim 13, wherein saidpredetermined format employs a multicarrier signal formed by a unitwhich includes subcarriers of a predetermined number and said time slotsof a predetermined number.
 17. The communication method according toclaim 13, wherein said predetermined format is a code division multipleaccess format.
 18. The communication apparatus according to claim 13,wherein a processing in said lowering step is carried out by loweringsaid information transmission rate in a communication path between saidfirst and said second apparatus without varying a capacity of saidcommunication path.
 19. The communication apparatus according to claim13, wherein a processing in said lowering step is carried out bylowering said information transmission rate per unit of communicationpath between said first and said second apparatus while increasing acapacity of said path.
 20. A communication apparatus for communicatingin a predetermined bandwith with a predetermined format for multipleaccess by each cell, comprising:communicating means for communicatingwith a predetermined station; information receiving means for receivinga predetermined communication status information from a third station;and rate adjusting means for lowering an information transmission rateof said communication when an output signal from said communicationapparatus indicates that said communication apparatus is located at anedge of a cell where said predetermined station is located and when anoutput signal from said information receiving means indicates that saidcommunication apparatus is approaching a cell where said third stationis located.
 21. The communication apparatus according to claim 13,wherein a common frequency band for communication is employed in a cellwhere said predetermined station belongs and a cell where said thirdstation belongs.
 22. The communication apparatus according to claim 20,wherein said predetermined format employs a multicarrier signal formedby a unit which includes subcarriers of a predetermined number and timeslots of said predetermined number.
 23. The communication methodaccording to claim 20, wherein said predetermined format is a codedivision multiple access format.
 24. The communication apparatusaccording to claim 20, wherein a processing in said lowering step iscarried out by lowering said information transmission rate in acommunication path between said first and said second apparatus withoutvarying a capacity of said communication path.
 25. The communicationapparatus according to claim 20, wherein a processing in said loweringstep is carried out by lowering said information transmission rate perunit of communication path between said first and said second apparatuswhile increasing a capacity of said path.